Mostly science, some physics teaching

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Author Archives: Richard Sear

I currently have 50 reports, and two dissertations to mark, and on Thursday next week I’ll have not one but two exam papers to mark. So I am taking a break from the endless marking to share with you something surprising that I have learnt, not about science but about history. My sister bought me The Silk Roadsby Peter Frankopan, for Christmas, and I am enjoying reading it. The book mentions the Ivy League (i.e., posh, presitigious and expensive) Yale university in the north east of the United State, although it omits the Elihu Yale Wetherspoons pub (i.e., pub that is not posh, lacks prestige but has cheap beer) in Wrexham in north east Wales.

As I write the UK politics is in a bit of a mess. The referendum that kicked off this mess started in the actions of an Eton educated posh boy: David Cameron. But not all Eton educated posh boys have been a disaster for Britain. The picture above is of the partially-Eton-educated 3rd Baron Rayleigh, a brilliant late-Victorian scientist and genuine member of the aristocracy. Continue reading →

Above is an image taken from a BBC webpage What is diffusion?– part of their Bitesize website, and aimed at 11 to 14 year olds*. So if you are from the BBC and you don’t like me using it, then just let me know and I will take it down, but the image on that page is fundamentally misleading, as I will explain. So arguably it should not appear on the BBC’s website either.

I am currently teaching biological physics to third-year physics undergraduates. As part of this I teach about how living organisms acquire food molecules, oxygen etc, and how large living organisms, such as ourselves, transport these food molecules, oxygen, etc around our bodies. A fundamental point that I make, is that diffusion is only fast enough to support the demands of life when the movement is over very small distances, around 1 mm or less. Over distances more than very roughly 1 mm, some sort of flow is required to move molecules around. Over distances of centimetres, metres and above, diffusion is very very slow.

One of the most useful skills we teach on the physics degree is data analysis. This is important in almost all scientific research, and it is also key to good decision making in other fields such as economics, as well as being a core part of data science — increasing numbers of our graduates are going into the growing number of careers as data scientists. One basic task in data analysis is fitting a model to noisy data, eg fitting a straight line y = mx + c to data of the form a set of points (x , y). As far as I know there is essentially complete consensus about how to determine the best values of the two fit parameters, the intercept c and the slope m. This is to minimise the sum of the squared differences between the fit function, and the data points.

I have just gotten back from the 3rd Sir Sam Edwards – New Horizons in Soft matter meeting. The meeting has an emphasis on bringing together soft matter scientists from universities and companies. As a university-based scientist it is fascinating to hear of the soft matter challenges companies face.

These vary from turning tons of potatoes into crisps, to making cosmetics that are sold for silly money.

I have just finished reading Outnumbered by David Sumpter. It is very readable, and says some interesting things about modern machine learning. Machine learning, in particular deep learning, is a hot topic at the moment, so I was curious to read about it, and about related stuff like how Facebook, Google, etc, use it.

Adults are recommended to eat about 2000 kilocalories per day. As this is an energy divided by a time it is a power consumption, and in the proper units, it is about 100 Watts. The power consumption of our bodies is a pretty basic feature of how our bodies work, but there is not much known about why a 80 kg guy like me needs 100 W, not 10 or 1000 W. We know* our brain needs of order 10 W, and our heart about 1 W, but for example we have only a poor idea of why our brain burns through 10 Joules every second. Continue reading →

Over the summer I am thinking a bit about how proteins and other stuff move around inside our cells, and those of other living organisms. I am trying to do this quantitatively, and so I need numbers for various aspects of living cells and of organisms. So I was delighted to find that there is an entire searchable website just for numbers related to living organisms, called, sensibly enough, BioNumbers, plus a related book: Cell Biology by the Numbers, by Ron Milo and Rob Phillips. Both websites are a mine of useful information. For example, one entry is the total length of fibres of the protein collagen in our bodies. The total length is about 100 billion kilometres, or to put in another way, in each of our bodies there is enough collagen to go from the Earth to the Sun 10,000 times.

Last year, Chrétien et al. published a paper in PLOS Biology on mitochondria. Two mitochondria are shown above, they are structures inside our cells where a key part of our energy metabolism take place. I don’t want to be harsh, but the central claim of their work is clearly wrong. This claim is that the mitochondria inside cells are at a temperature of around 50 C, more than 10 C higher than the rest of the cell which is about 37 C. This really cannot be right, the mitochondria inside your body are at the same 37 C that the rest of you is, and with a little physics it is easy to see why.